|Research Area||Materials Science|
|Principal Investigator(s)||Dr. Andrea Fratalocchi|
The early days of 21st century are experiencing a revolution in synchrotron source intensities driven by the new generation of X-ray Free Electron Lasers (XFEL). Such sources will be able to deliver femtosecond pulses of peak powers above 100GW, characterized by atomic-scaled wavelengths and a high degree of spatial and temporal coherence. This opens in the near future the possibility to perform single molecule experiments, involving the real-time reconstruction of molecular images from diffraction patterns recorded at x-rays. However, the physics behind such phenomena, at the intensities reached by XFEL sources, is in many respect unknown. In particular, the most problematic issue concerns the problem of radiation damage of samples exposed to intense XFEL radiation. The process is triggered by the XFEL photoionization of core electron shells that, in turn, either escape or decay through Auger relaxation, forcing the system to accumulate a strong positive charge around the nucleus. This results into an abrupt explosion of the atom as due to the unbalanced Coulomb forces mutually exerted by the ions. A quantitatively analysis of this process, which is fundamental for the next generation of imaging experiments, is still lacking.
The ACES-X project employs a massively parallel numerical approach to deal with this problem. Our ab-initio theory makes use of molecular dynamics for ions evolution, of time-dependent density function theory for electrons dynamics and of nonlinear finite-difference time-domain methods for the exact propagation of electromagnetic waves. This approach will allow for the real-time simulation of Coulomb explosion with reference to realistic samples, as well as the theoretical determination of the ionization intensity and optimal pulse length for the next generation of molecular imaging experiments.